frontend-repo/public/WEB-INF/web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.0" metadata-complete="true">
<display-name>Router for Tomcat</display-name>
  <error-page>
  <error-code>404</error-code>
  <location>/index.html</location>
  </error-page>
</web-app>